Several systems of operating and locking mechanisms for railroad switches or "points" exist in various different countries and depending on the functions that are to be performed, in particular on whether the switch is capable of being burst open or "trailed". A switch which is capable of being trailed is one which, when used as a trailing switch, i.e. when approached from the direction having two tracks leading to a single track, passes traffic, without damage, coming from the track which does not correspond to the direction in which the switch is set, with the switch then being displaced by axle thrust. When a switch is approached by traffic coming from the single track and going towards one of the plurality of different tracks, the switch is said to be a facing switch. A switch includes two moving blades, referred to as a right point blade and as a left point blade. The terms "right" and "left" correspond to the positions of the point blades as seen when the switch is approached as a facing switch. One of the blades touches its corresponding backing rail, while the other blade is at a distance from its backing rail.
French switches are not trailable, whereas the switches on German lines are trailable. French switches which are used as trailing switches only or which are used as facing switches at speeds not exceeding 40 km/h, have a motor system including an guide plate and drive wheel system internal to the motor for locking the switch in each of its two positions. For switches used as facing switches at speeds in excess of 40 km/h, French railways make use, in addition, of an external, direct-action locking system for each blade individually, with such locking systems being known in France as "carter-coussinet" locks. These systems have only one drive rod actuating both the right and the left point blades.
German switches are trailable. One prior operating mechanism with internal locking includes an outlet shaft provided with two special gear wheels each meshing with the rack of a corresponding drive rod.
One of the drive rods is connected to the right point blade and the other is connected to the left point blade. The touching blade is locked by means of a locking bar which penetrates, at the end of outlet shaft rotation and at the end of drive rod displacement, in a notch provided in the drive rod of the touching blade. The mechanism is reversible when trailed, by acting on the non-locked non-touching blade which is held in place by a force from a torque limiter.
In addition to providing mechanisms for operating and locking a switch, it is also necessary for safety purposes to check the actual positions of the blades at the end of a switching operation.
In France, this checking is performed by checking devices fixed on the blades themselves for switches which are used solely as trailing switches. For switches that may be used as facing switches and including the so-called "carter-coussinet" locking system, the locking system itself includes devices for checking the presence and the locking of the touching blade.
In other countries, a known system consists in operating and locking the blades by two bars each fixed to one blade, with the two blades being interconnected by a spacer bar and with the position of the blades being checked by means of two other bars which convey position information to a checking device which may be integrated in the motor or otherwise.
In this case, the switch has a four-bar motor-and-checking unit, whereas in France the switch has a motor with an internal locking system using a guide plate and a drive wheel, plus external locking by means of "carter-coussinet" locks, plus the checking devices.
The object of the present invention is to provide a point motor system capable of performing all the required functions with intrinsic safety by means of two bars only, and providing a greater degree of safety than the present French system using "carter-coussinet" locks together with checking devices. The proposed motor system is also simpler and cheaper than said prior system and than foreign four-bar systems.
The invention is applicable to a railroad switch which is not trailable and which has two locked blades.